Half-differential short-circuit ring encoder
A semi-differential short-circuit ring sensor (HDK) is an angular position sensor ( distance sensor ) for regulating the fuel quantity in diesel engines .
Electronically controlled axial piston distributor injection pumps are used as part of the electronic diesel control . To regulate the injection quantity, which varies depending on the speed, the opening time of a so-called control bore is controlled by a control slide on the distributor piston. Depending on the rotation of the control shaft, the control opening is released sooner or later via an eccentric and thus the fuel is returned sooner or later - this determines the injection quantity. The control unit needs information about the angle of the control shaft. A simple potentiometer transmitter has the disadvantage that mechanical wear occurs.
The semi-differential short-circuit ring encoder (HDK) works without contact and is therefore wear-free. It consists of a soft iron core (light gray in the picture), measuring coil (L1) and a movable short-circuit ring (left, red). Its currents limit the magnetic flux to the space between the coil and the short-circuit ring. If this is shifted by the control shaft, the magnetic flux changes and thus the inductance of the measuring coil. The right side of the HDK sensor with the reference coil (L2) has a symmetrical structure, but has a fixed short-circuit ring (half-differential arrangement). It serves as a reference for temperature compensation , for adjustment with respect to the measuring coil and to compensate for material properties. The measuring range of the 30 mm diameter sensor is 0–60 °.
Short-circuit ring encoder
The functional principle is based on changing the magnetically effective air gap . The control unit sends a constant sinusoidal alternating current at 10 kHz through the coil L1, which generates a current in the short-circuit ring which, according to Lenz's rule, builds up a magnetic field that counteracts the cause and limits the magnetic flux to the area between the coil and the short-circuit ring. This changes the reluctance of the magnetic circuit and, accordingly, the inductance of the coil. The soft iron core is shaped in such a way that the inductance is almost linearly dependent on the position of the short-circuit ring. An alternating current of the same frequency flows through the coil L2, the voltage of which is compared with the voltage across L1 ( ratiometric measurement).
The control unit monitors the function of the coils for errors, provides an analog output voltage and a 12-bit data word for the angle of the control shaft at the output.
Linear design
Semi-differential short-circuit ring encoders are also used in a straight version to measure the position of the control rod of diesel in-line injection pumps. The soft iron core (light gray in the picture) is then straight and the short-circuit ring is moved in a straight line. The linear measuring range is approx. 30 mm.
swell
- ↑ a b c Reif, Konrad: Classic diesel injection systems: in-line injection pumps, distributor injection pumps, nozzles, mechanical and electronic controllers. Springer-Verlag, 2012, p. 124, ISBN 9783834886644 , chapter semi-differential short-circuit ring sensors in the Google book search
- ↑ Data sheet circuit CC 215
- ↑ Bauer H., Berger J., Fischer W., Wannenwetsch P .: Further development of the electronically controlled distributor injection pump system. In: Motortechnische Zeitschrift No. 53, 1992, pp. 240–245 ( PDF 5.7 MB).
- Expertise in automotive engineering. 28th edition. Verlag Europa-Lehrmittel, Haan-Gruiten 2004, ISBN 3-8085-2238-0 , p. 300.
- E. Zabler, F. Heintz: Short-circuit ring sensors as versatile position and angle sensors in motor vehicles. In: NTG reports. Volume 79, 1982, pp. 213-221.
- Patent US5248938 : Inductance Type Rotational Position Sensor Including A Magnetic Core Having Fixed and Movable Short Rings. Applicant: Asmo Co. LTD, Inventor: Kobayashi et al. (Explanation of the functional principle in English).